The present invention relates to a pumping device comprising a tank containing a fluid to be pumped, a main pumping stage for pumping a controlled amount of said fluid at a predetermined pressure, and a supply pump for supplying fluid from said tank to said main pumping stage in excess to said controlled amount.
Pumping devices of the aforementioned type are employed, for example, when the main pumping stage is in the form of a high-pressure pump. In this case the supply pump provides for ensuring at all times sufficient fluid flow, preferably at a sufficient predetermined pressure, to the intake portion of the high-pressure pump.
A pumping device of the above type is described, for example, in EP-A-0299337, which relates to a pumping device for a motor vehicle fuel injection system. In this case, the supply pump is connected to a parallel pressure relief valve by which any excess fluid is fed directly back to the tank.
Depending on power and output pressure, the main pumping stage is subjected to more or less severe mechanical and/or thermal stress, which, with a main pumping stage output pressure in the order several hundreds bar, may be so severe that steps must be taken for controlling or limiting said stress.